Geochemistry 428/628
Exam 3 sample questions

The final exam will concentrate on material covered since the last exam. It will include basic concepts of geochemical modeling, and will include questions based on your class presentations! A class like this inherently builds on concepts discussed earlier in the semester, so by definition, it is cumulative.

Example Questions

  1. What are delta-D and delta-18O?
  2. Describe and account for the measured delta-D and delta-18O in meteoric water across North America.
  3. Describe a way oxygen isotopes can be used as a paleothermometer.
  4. Why do water and steam in geothermal areas usually display a delta-18O shift, but not a delta-D shift?
  1. Weathering of pyrite-bearing shales in North Dakota might lead to the formation of the sulfate mineral
    potassium jarosite, KFe3(SO4)2(OH)6. Write a balanced equation for the reaction pyrite --> jarosite.
    (Obtain K from the environment).
  1. What is pe, and how is it related to Eh? How is it measured?
  1. Consider the Eh-pH diagram given in Faure, Fig. 21.1a.
  2. Write the chemical reaction between tenorite (CuO) and Cu2+ in terms of water and hydrogen ion.
  3. Derive the Eh-pH equation for this reaction.
  4. What concentration of Cu2+ would be found in a lake having an Eh = 0.40 and pH = 7.5?
  1. In his classic study of the saprolites formed on granitic gneisses in Minnesota, Goldich observed that potassium feldspars weather more slowly than plagioclase feldspars. What could be a reason for such a phenomenon?